In an electrical distribution system of a large facility, switchgear is the connection between the power source and the circuits that distribute power to the equipment. The switchgear is an assembly containing electrical switching, protection, metering and management devices for industrial, commercial, and utility applications. A motor control center is a switchgear application designed to control and protect a large facility's motors. Plant supervisory management systems or Programmable Controllers (PC), or Programmable Logic Controllers (PLC) are process control systems which control electrical switching, protection, metering and management devices in switchgear applications. PCs, PLCs and plant supervisory management systems communicate directly with the devices or processes such as pushbuttons, switches, sensors, control alarms, and starters. The information supplied to the process control systems may include data about each circuit such as status data, current and voltage in each phase of a multi-phase distribution system, electric power, phase angle, trip setting of the circuit breaker, and current reached during trip events. The data can be in the form of discrete inputs/outputs (I/O) such as ON/OFF, or open/closed, as well as data I/O such as current outputs, and voltage outputs.
In a typical switchgear installation, there is a need for communication between different control systems and processors from various manufacturers and utilized in the installation. Historically, process computer manufacturers have developed fieldbus protocols and data structures without regard to standardization. As used herein, the term Fieldbus means special form of local area network dedicated to applications in the area of data acquisition in an industrial or manufacturing facility. The network may, for example, be a digital, bi-directional, multi-drop, serial-bus, communications network used to link isolated field devices such as controllers, transducers, actuators, and sensors on the factory floor. Protocols are implemented in process computers to effect the orderly exchange of information between the components. Standardization of protocol convention typically determines the nature of the data representation, the format of the data representation over a communication path, and the sequence of any control message that are to be sent. The procedure of the standard protocol must be maintained by both destination computers in a communication link.
Since many manufacturers have not adopted standard protocols, as explained above, and in order to achieve compatibility between the various incompatible data formats from different manufacturers, switchgear systems have often relied on firmware residing in the PLCs or a separate interface system to communicate with the PLCs and the devices. The firmware is tailored to interface between the various incompatible systems operating at varying data rates and with varying data formats. For example, one system only accepts small "chunks" of data of less than 16 bits because of its limited communications capability, whereas other control systems require a minimum data length of 16 bits for each data chunk. Some control systems supply data and instructions in only one bit, e.g., for switch ON/OFF, whereas the field devices need two bits for switching. There is also a need to tailor the data to meet the customers' specific requirements such as cutting off overhead data so as to display only certain amount of data, or transmitting/displaying data in a particular format. Some customers are only interested in status bits, such as whether the drives in the system are ON/OFF or tripped. Other customers need to know the currents because of the extra maintenance functions implemented in their plant supervisory management system. In addition, when new units are added to the system or existing units are changed, it often becomes necessary to redo the firmware package with the firmware being reprogrammed or enhanced by a lengthy process including a complete test and verification cycle. This results in many incompatible, and sometimes unmanageable, firmware releases to meet the customers' special applications.
From the vendors' point of view, it is desirable to build a data selector/formatter, i.e., an interface system between the process control computers and the devices, without having to make multiple modifications and test and verification programming cycles, which system also enables customers to specify the amount of information to be provided and the data formats needed. By transferring only requested data via the interface system, the load on the plant supervisory management system can be reduced.
Therefore, it is an objective of the present invention to provide a communication interface driver for switchgear applications which is an application-independent module for separating the communication interface drivers from the application software, and for selecting and translating data exchanged between the field devices and the process control computers.
It is another object of the present invention to provide a communication interface system which is based on communication objects such as data and function objects.
A still further object and advantage of the present invention is a dynamic and open configurable interface system for switchgear applications with interchangeable sets of communication and interface driver modules.